Since the Multiple Input Multiple Output (MIMO) technology can increase system capacity, improve transmission performance, and be well integrated with other physical layer technologies, it becomes a key technology of Beyond third Generation (B3G) and fourth Generation (4G) mobile communication systems. However, when channel correlation is strong, the diversity gain and multiplexing gain due to a multipath channel will be greatly reduced, thus resulting in largely reduced performance of a MIMO system.
There is a new MIMO precoding method in the related art, which is an efficient mode of MIMO multiplexing. This method divides a MIMO channel into a plurality of independent virtual channels through precoding processes at a receiver and a transmitter. Since the effect of channel correlation is effectively eliminated, the precoding technique guarantees stable performance of the MIMO system in a variety of environments.
The Long Term Evolution (LTE) system is an important project of the Third Generation Partnership Project (3GPP). FIG. 1(a) and FIG. 1(b) are diagrams of frame structures for a Frequency Division Duplex (FDD) mode and a Time Division Duplex (TDD) mode of the LTE system, respectively.
In the frame structure of the FDD mode shown in FIG. 1(a), a radio frame of 10 ms is composed of twenty time slots with a length of 0.5 ms each, numbered from 0 to 19, and time slots 2i and 2i+1 compose a subframe i with a length of 1 ms.
In the frame structure of the TDD mode shown in FIG. 1(b), a radio frame of 10 ms is composed of two half frames with a length of 5 ms each, and a half frame contains five subframes with a length of 1 ms each. The subframe i is defined as two time slots 2i and 2i+1 with a length of 0.5 ms each. Wherein, a special subframe contains three special time slots, namely, a Downlink Pilot Time Slot (DwPTS), a Guard Period (GP) and an Uplink Pilot Time Slot (UpPTS), of which a proportion relationship in a subframe has a total of nine configurations as shown in the following Table 1, wherein, Ts is a sampling frequency.
TABLE 1configurations of special time slots in a special subframeUsing a normal cyclicUsing an extended cyclicprefix for the downlinkprefix for the downlinkUpPTSUpPTSUsing aUsing anUsing aUsing annormalextendednormalextendedconfigurationscycliccyclic prefixcycliccyclic prefixof a specialprefix forfor theprefix forfor thesubframeDwPTSthe uplinkuplinkDwPTSthe uplinkuplink0 6592 · Ts2192 · Ts2560 · Ts 7680 · Ts2192 · Ts2560 · Ts119760 · Ts20480 · Ts221952 · Ts23040 · Ts324144 · Ts25600 · Ts426336 · Ts 7680 · Ts4384 · Ts5120 · Ts5 6592 · Ts4384 · Ts5120 · Ts20480 · Ts619760 · Ts23040 · Ts721952 · Ts———824144 · Ts———
In the two frame structures, when the system uses the Normal Cyclic Prefix (Normal CP), a time slot has a length of seven uplink/downlink symbols; and when the system uses the Extend CP, a time slot has a length of six uplink/downlink symbols. The aforementioned symbols are Orthogonal Frequency Division Multiplexing (OFDM) symbols.
A Resource Element (RE) is a sub-carrier on a OFDM symbol, while a downlink Resource Block (RB) consists of twelve consecutive sub-carriers and seven (six when the Extended CP is used) consecutive OFDM symbols, which is 180 kHz in the frequency domain, and has a length of a general time slot in the time domain, as shown in FIG. 2. The LTE system allocates resources with a RB as a basic unit during the resource allocation.
The LTE system supports a MIMO application of four antennas, and corresponding antenna port #0, antenna port #1, antenna port #2 and antenna port #3 adopt a mode of full bandwidth Cell-specific Reference Signals (CRS). When the CP is the Normal CP, locations of these CRSs in a physical RB are shown in FIG. 3(a). When the CP is the Extended CP, locations of these CRSs in a physical RB are shown in FIG. 3(b). In FIG. 3(a) and FIG. 3(b), abscissa 1 refers to serial numbers of subframes in the OFDM symbol, i.e., C1, C2, C3 and C4, which correspond to the logical port #0, the logical port #1, the logical port #2 and the logical port #3 of the CRSs.
In addition, there are UE-specific reference signals, which are only transmitted on locations in the time-frequency domain where the user-specific Physical Downlink Shared Channel (PDSCH) is. Wherein, functions of these CRSs comprise downlink channel quality measurement and downlink channel estimation (demodulation).
The advanced long term evolution (Further Advancements for E-UTRA,LTE-Advanced or LTE-A) is an evolution version of LTE Release-8. In addition to meeting or exceeding all relevant requirements of 3GPP TR 25.913: “Requirements for Evolved UTRA (E-UTRA) and Evolved UTRAN (E-UTRAN)”, IMT-Advanced requirements proposed by the International Telecommunications Union-Radio (ITU-R) are required to be achieved or exceeded. Wherein, requirements of backward compatibility with the LTE Release-8 refer to that terminals of the LTE Release-8 can operate in a LTE-Advanced network; and terminals of LTE-Advanced can operate in a LTE Release-8 network.
Additionally, LTE-Advanced should be able to operate under configurations of different size spectrums, including a configuration of a spectrum wider than that of the LTE Release-8 (such as consecutive spectrum resources of 100 MHz), so as to achieve higher performance and a higher target peak rate.
Since the LTE-Advanced network needs to be able to access LTE subscribers, an operational band of the LTE-Advanced network should cover the current LTE band, while there is already no consecutive spectrum bandwidth of 100 MHz which can be allocated in the band, and therefore a direct technology to be addressed by the LTE-Advanced is to aggregate a plurality of consecutive component carrier frequencies (spectrums) distributed in different bands by means of a component carrier technology, to form a bandwidth of 100 MHz which can be used by the LTE-advanced. That is, the aggregated spectrum is divided into n component carrier frequencies (spectrums), and the spectrum within each component carrier frequency (spectrum) is consecutive.
In the LTE-Advanced requirement study report TR 36.814 V0.1.1 proposed in September 2008, it is explicit that the downlink of the LTE-Advanced can at most support an application of eight antennas. For the purpose of supporting the application of 8 antennas and using techniques such as Coordinated Multiple Point (CoMP), dual stream beamforming, etc., a basic framework (way forward) for designing downlink reference signals of the LTE-Advanced is determined for the LTE-Advanced at the 56th conference of 3GPP in February 2009. The downlink reference signals operating the LTE-Advanced are defined as two types of reference signals, i.e., a PDSCH demodulation oriented reference signal and a Channel State Information (CSI) generation oriented reference signal. Moreover, the PDSCH demodulation oriented reference signal is transmitted based on layers, and each layer corresponds to a kind of reference signal. The maximum of layers supported in the LTE-Advanced system is eight.
At present, time frequency locations of reference signals about two layers in a subframe have already been determined, as shown in FIG. 4(a) and FIG. 4(b), and there are two modes for mapping a sequence, i.e, mapping a sequence to the frequency domain first and then the time domain; alternatively, mapping sequences one by one according to the physical RBs, and then mapping the sequences to the frequency domain and then the time domain, in the physical RBs. However, both schemes have no specific implementation method, and therefore, it is necessary to provide a specific implementation method, so as to guarantee an application of multi-antenna transmission functions.